U.S. Pat. No. 4,625,712 discloses a miniature multi-stage axial-flow blood pump which can be percutaneously inserted into an artery for emergency heart assist. The pump is driven by a cable from a motor outside the body and provides a continuous blood flow of several liters per minute at high operating speeds.
In the course of research aimed at providing higher flow rates and even higher operating speeds with minimal hemolysis and increased safety, it has been found that the multi-stage design of U.S. Pat. No. 4,625,712 was not fully satisfactory because of limitations imposed by the allowable amount of hemolysis. On the other hand, conventional design wisdom indicated that single stage pumps could not be used because of the limitations in pressure rise per stage inherent in axial flow pumps.
Also, a problem arose from the fact that blood-compatible materials for the cable sheath were not sufficiently abrasion-resistant to safely allow prolonged operation of the pump.